The axial heat transfer coefficient during flow boiling of n-hexane was measured using infrared thermography to determine the axial wall temperature in three geometrically similar annular gaps with different widths (s = 1.5 mm, s = 1 mm, s = 0.5 mm). During the design and evaluation process, the methods of statistical experimental design were applied. The following factors/parameters were varied: the heat flux _ q = 30 À 190 kW=m 2 , the mass flux _ m = 30 À 700 kg=m 2 s, the vapor quality _ x = 0:2 À 0:7, and the subcooled inlet temperature T U = 20 À 60 K. The test sections with gap widths of s = 1.5 mm and s = 1 mm had very similar heat transfer characteristics. The heat transfer coefficient increases significantly in the range of subcooled boiling, and after reaching a maximum at the transition to the saturated flow boiling, it drops almost monotonically with increasing vapor quality. With a gap width of 0.5 mm, however, the heat transfer coefficient in the range of saturated flow boiling first has a downward trend and then increases at higher vapor qualities. For each test section, two correlations between the heat transfer coefficient and the operating parameters have been created. The comparison also shows a clear trend of an increasing heat transfer coefficient with increasing heat flux for test sections s = 1.5 mm and s = 1.0 mm, but with increasing vapor quality, this trend is reversed for test section 0.5 mm.
In this article, a novel form of thermal interface material (TIM), represented by three industrially manufactured pressure-sensitive adhesive (PSA) tapes with electrical insulating properties, is characterized regarding its applicability in an electric motor with air-gap winding. Firstly, the adhesion performances, in terms of the winding process, were investigated experimentally. Here, every TIM shows sufficient shear strength for the wire–TIM joints, as well as peel adhesion to the laminated iron core. Secondly, the thermal–physical properties of the TIMs are inspected experimentally via laser flash analysis (LFA) and differential scanning calorimetry (DSC). For every TIM, the value of the thermal resistance can double if the relatively smooth surface (Ra = 0.2 μm) of the adjacent layers is interchanged with a rougher one (Ra = 2.0–3.7 μm). Additionally, the TIM’s performance at the system level is examined. Therefore, a flat test section, according to the specifications of the original motor, is studied experimentally and numerically utilizing infrared (IR) thermography and the finite element method (FEM). The focus is set on the heat flow and temperature distribution in the test section under varying thermal loads, mass flow, and variety of TIMs.
Engine waste heat recovery represents one of the main advantages of a gas engine heat pump (GEHP) as compared to conventional heat pump system. Engine waste heat can be recovered to heat the supply water (at high ambient air temperature) or to evaporate the refrigerant in the refrigerant circuit (at low air ambient temperature). At the middle range of ambient air temperature (10:15°C), the two possibilities are valid but the GEHP performance is different. The present work is aimed at comparing the performance characteristics of the gas engine heat pump with waste heat recovery subsystems for supplying the hot water demands. In order to achieve this objective, a test facility was developed and then experiments were performed over a wide range of condenser water inlet temperature (34°C to 48°C) and at ambient temperature of 13°C. Performance of the gas engine heat pump was characterized by the supply water outlet temperature, heating capacity, gas engine energy consumption and primary energy ratio. The results showed that a water outlet temperature up to 70°C is obtained when the recovered engine heat is transferred to the supply water circuit. On the contrary, a higher condenser heating capacity (13%) and higher gas engine energy consumption (12.8%) are obtained when the recovered engine heat is transferred to the refrigerant circuit. Furthermore, primary energy ratio of the gas engine heat pump is increased by 17.5% when recovered engine heat is transferred to the supply water circuit. Also, GEHP incorporated with heat recovery subsystems can be used for utilizing the waste heat to provide efficient supply of hot water.
"Lithium-ion batteries currently used in electric vehicles have strong thermal limitations. Thus, both excessively high and low temperatures lead to an accelerated aging process in form of capacity losses through SEI-layer buildup on the one hand and lithium-plating on the other hand. Additionally, temperature gradients within a cell, as well as temperature differences between individual cells have to be minimized in order to increase the system’s durability. With a properly designed battery-thermal-management (BTM), not only the aging process can be minimized but also extreme cases like thermal runaways can be prevented, which otherwise can cause fatal ecological and economical damage or in the worst-case-scenario exposes and harms vehicle occupants to fire, explosion or intoxication due to a damaged battery cell system. For the application of an efficient BTM, a detailed characterization of the battery’s thermal behavior during the charge and discharge cycle with different loads is essential. This paper deals with high-performance pouch cells, as they have a favorable ratio of heat transfer surface area to battery volume for BTM. However, they also present a particular challenge for the acquisition of the surface temperature distribution, as they do not have a solid shell. An external force must be applied to this cell type to prevent it from inflating, when it is under higher loading conditions, because this volume change is expected to change the cell’s thermal behavior. Therefore, the determination of the surface temperature in the present study was carried out while the cell was fixated and forced to stay in its geometric shape. The mechanical fixation has an influence in the thermal behavior and therefore the temperature distribution should be probed in this configuration but this also makes the optical measurement of temperature more difficult as pressure transmission plates must be made transparent. The measured surface temperature distribution can then be used as an input for a FEM-simulation to provide information on the whole cell’s internal temperature field. To the authors´ knowledge, no thermal investigations in this configuration have been reported. Two different optical temperature measurement methods are applied. The first technique is IR-thermography, which is based on the measurement of heat radiation from the surface, and which is restricted to regions on the surface using small IR-transmitting sapphire windows. The second technique, phosphor thermometry, exploits the temperature dependent luminescence properties of thermographic phosphor materials. The phosphors are applied as a thin coating on the surface of the battery and illuminated by a light source. The resulting luminescence emission in the visible range is detected to infer the temperature of the whole surface, since normal glass can be used. The surface temperature distribution obtained by these two techniques are provided and the advantages or disadvantages of each technique are described in terms of precision, accuracy, sensitivity, temporal resolution, spatial resolution and also implementation expenses. The internal temperature field provided by the heat transfer model for a known surface distribution is also presented and the impact of this integral thermal characterization on the BTM is discussed."
The experimental results concerning heat transfer characteristics and flow pattern visualization in narrow annular gaps will be presented. On this account, experiments were carried out using two different test sections. An outer heated concentric annulus allowed the calculation of the heat transfer coefficients through the measurement of the outer wall temperatures using infrared thermography. On the other hand, an inner heated annulus with an outer glass tube, having the same gap size, 500 μm, was employed for flow observations using a high speed camera. By these means, both measurement methods can be combined in order to correlate the trends of the heat transfer coefficients as function of vapor quality with the observed boiling regimes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.